Antenna near field intensity prediction

Situations arise where several systems operate in close proximity on a given platform like an armoured carrier, aircraft carrier, or an aircraft. In some of these systems, like radar, the radiated RF powers are high and due to close proximity with other systems, high field intensities are likely to get coupled to them through antenna to antenna coupling, antenna to box coupling, and antenna to wire coupling. For EMI prediction it is necessary to have an assessment of the coupled fields within the near field ranges of large antennas for which antenna near field prediction is required. The emitted EM fields in close proximity to the aperture are reactive, their free space impedance different than 120π and the E and H field phase relationship not well defined as it is in case of the far field regions. An analysis is carried out to bring about a closed form solution for the prediction of the EM fields in the near field regions of the antennas such that the results are amenable to computer coding for automated prediction analysis. For this analysis two procedures are presented. The first one is based on the far field to near field transformation using spherical wave expansion. The other is for less accuracy, yet is simpler for the computation of the near fields of a large antenna. This method is based on a notional array with antenna parameters like gain beam widths and sidelobes similar to the antenna under consideration.